Those of you who live where the mercury doesn't regularily hang out in the minus 20's and below, probably never get to experience the joy of a frozen sewer vent, something that happens up here several times over the course of the winter. Sewer systems usually have a vent up on the roof, letting all of the noxious gases escape out of the house, rather than in the washroom or elsewhere. Of course these gases are nice and warm and moist, and when they hit cold winter air they freeze, usually building up over time and eventually capping off the vent. That means that the sewer gas (and remember in our case it is a nice warm sewer tank below the house that is generating the gas) has no where to go and soon the house smells like, well, like a sewer tank.
Normally the solution is to get out a ladder and crawl up on to the roof with a kettle of boiling water and/or something to chip away the ice and open up the vent that way. But our roof is way too dangerous for that method. The sewer vent is probably about 35 feet up, and the roof is slippery metal, pitched at almost 30 degrees (28.41 degrees to be a little more precise).
Our solution is quite elegant actually, (and when I say "our" I mean I nodded enthusiastically when Gary and Dale thought about it). First of all the roof where the vent is located is uninsulated around the pipe. This allows heat from the house to warm the vent stack and keep ice from forming in it. This is only a partial solution as the gas still freezes when it meets the cold air and the ice forms outside the vent, still building up and blocking. The second part of the solution was to bring the stack straight down into a clean out and branching the stack off from there. This clean out is in the attic.
So when the vent freezes over, as it did again today for about the fifth time this winter, I simply go up into attic and take the cap off the clean out (holding a bucket underneath to collect the condensed, er, water). I then use a long stick to punch out the ice from below, opening the vent once more. The technique still needs some refinement, I need to come up with a better "chisel", as frequently I just punch a small hole in the ice, which quickly freezes up again, but all in all it sure beats climbing up onto that roof in -35 degree weather, hoping I'd hit a snowbank on the way down.